How to fix the bone influencing other meshes
In Edit mode, select the vertex, open the N panel, you'll see if the vertex is part of a vertex group it is not supposed to be part of, you can remove if from this group if you press the X button.

Blue doesn't mean the selected bone or group has no influence on these vertices, it might be a very low influence, to check the real zero influence in Weight Paint mode you need to display the Zero Weight option of the Viewport Overlays.